How to do usability testing without users?
You can use a heuristic evaluation to evaluate the user experience without observing user behavior directly. In a Heuristic Evaluation, an expert reviews the interface against a set of guidelines or principles (heuristics), which provide a template to uncover problems that a user will likely encounter.
Why is it important to get users involved in testing?
User testing allows product teams to discover usability and design issues with their products before they go to the larger market. It's important to discover these type of issues early as opposed to when they have been exposed to the larger market.